Polyimide resins from bis-imide, monomer having two methylene groups activated by adjacent carbonyls, and polyamine

ABSTRACT

Polyimide addition copolymers of improved physical properties and thermal stability are prepared by reacting ethylenically unsaturated bis-imides with compounds having two methylene groups activated by adjacent carbonyl groups. The copolymers may be made in the presence of catalytic amounts of amines or with greater amounts of polyamines. The polymers are useful in producing molding powders, prepregs, laminates, circuit boards, encapsulants and metal clad shapes.

This is a continuation of co-pending application Ser. No. 06/881,853filed on July 3, 1986 now U.S. Pat. No. 4,822,870.

This invention relates to novel polyimide compositions for use instructural composites, reinforced laminates, prepregs, encapsulants andmetal or plastic film clad sheets. In particular the invention isdirected to addition copolymers with controlled cross-linking havinggood thermal stability which are made by reacting ethylenicallyunsaturated bis-imides with compounds containing at least two methylenegroups activated by two adjacent carbonyl groups.

In accordance with the present invention polyimide polymer compositionsare prepared which may be represented as having repetitive unitscharacterized by the idealized general Formulas I or II (see Table ofFormulas) wherein B and Z may be selected from various divalent radicalsand wherein at least one R', R² is --H, and the other is a halogen or analkyl group having one to four carbon atoms. R³ may be selected from thesame or different monovalent radicals such as hydrogen and alkyl,alkaryl and alkoxy groups having up to 30 carbon atoms. Under mostconditions only one active hydrogen on each methylene group is displacedas shown, however under more reactive conditions, a second hydrogen canbe displaced from the group to form addition products.

The resins of the invention are made by reacting diactivated dimethylenecompounds such as those selected from the general Formulas IIIa and IIIbwith N,N'-bis-imides selected from the general Formula IX where D is adivalent radical having a carbon-carbon double bond such as maleimidesselected from those having the general Formulas IVa and IVb. In thepresence of an amine catalyst the reaction proceeds to completion in arelatively short period of time at a low temperature. The polymerizationreaction can be conducted at a temperature of 0° to 200° C. andpreferably in the range of 50° to 150° C. The mol ratio of thediethylenically unsaturated imide of general Formula IX to the diactivedimethylene compound of general Formulas IIIa and IIIb in the reactionmix may range from 0.5/1.0 to 20/1.0 and preferably 0.5/1-3/1. As themol ratio approaches 1/1, copolymers containing higher molecular weightlinear segments between crosslinks may be prepared at temperatures belowabout 150° C. to control vinyl polymerization. This offers excellentcontrol of the physical properties of the resulting polymers and permitsthe synthesis of less brittle materials characteristic of mostpolyimides. Monoethylenically unsaturated imides of Formula IVb may beincluded in the reaction mix to control molecular weight.

The polymer of this invention can range in molecular weight from 500 to20,000 at the prepreg stage and higher when fully cured to the thermosetstage.

The reaction may be carried out neat or in a non-reactive organicsolvent system. Non-reactive organic polar solvents such asdimethylformamide, dimethylacetamide, 1-methyl-2-pyrrolidone,dimethylsulfoxide, or bis-methoxyethyl ether are preferable.

When polar solvents are used it is preferred to add to the system smallamounts of selected compounds which inhibit free radical or ionicpolymerization to stabilize the system and prevent gelation. Suchcompounds are benzoquinone, methane sulfonic acid, acetic acid andothers. Methane sulfonic acid in concentrations as low as 50 ppm willprevent gelation. In a properly selected polar solvent such as dimethylformamide the prepolymer results as a gel free viscous resin from whicha film can be cast.

The polymerization reaction may frequently benefit by the addition ofcatalytic amounts of weak nitrogenous bases such primary, secondary andtertiary amines and quaternary ammonium bases. The tertiary amines andthe quaternary ammonium bases constitute true catalysts. However,primary and secondary amines do also "catalyze" the reaction but alsobecome an integral part of the polymeric structure.

The amines which are used to catalyze the Michael reaction may berepresented by the general Formula VII and VIII wherein, R⁴, R⁵, R⁶ andR⁷ are independently hydrogen, and alkyl, cycloalkyl, aryl or anarylalkyl radical having up to 20 carbon atoms. Specific examples arelisted in Formula VI.

The N,N'-bisimides useful in the invention are well-known and may beconveniently prepared from anhydrides and diamines as described in U.S.Pat. No. 2,444,536. Briefly this process comprises reacting an anhydridewith a primary diamine to yield a bismaleamic acid. This bismaleamicacid is then cyclized with acetic anhydride using sodium acetate toyield the desired N,N'-bis-imide having the general Formula IX wherein Drepresents a divalent radical containing a carbon-carbon double bond andB is a divalent radical having at least 2 carbon atoms. (B) mayrepresent linear or branched alkylene radicals having less than 13carbon atoms, cycloalkylene radicals having 5 or 6 carbon atoms in thering, heterocyclic radicals containing at least one of the atoms O, Nand S, or a phenylene or polycyclic aromatic radical. These variousradicals may carry substituents which do not give undesiredside-reactions under the operating conditions. (B) may also represent anumber of phenylene or alicyclic radicals connected directly to oneanother or by a divalent atom or group such as, for example, oxygen orsulphur, and alkylene groups of 1 to 3 carbon atoms, or one of thegroups of Formula V in which R¹³, R¹⁴ and Y each represent alkyl groupsof 1 to 4 carbon atoms, or a cycloalkyl radical having 5 or 6 carbonatoms in the ring, or a phenyl or polycyclic aromatic radical, and Qrepresents a straight or branched alkylene radical having less than 13carbon atoms, a cycloalkylene radical having 5 or 6 carbon atoms in thering, or a mono- or polycyclic arylene radical. The radical D is derivedfrom an ethylenic anhydride of the Formula X which may be for examplemaleic anhydride, citraconic anhydride, and itaconic anhydride.

The preferred N,N'-bis-imide of Formula IX which may be employed aremaleic N,N'-ethylene-bisimide, maleic N,N'-hexamethylene-bis-imide,maleic N,N'-metaphenylene-bis-imide, maleicN,N'-paraphenylene-bis-imide, maleicN,N'-4,4'-diphenylmethane-bis-imide, maleicN,N'-4,4'-diphenylether-bis-imide, maleic N,N'-4,4'diphenylsulphone-bis-imide, maleicN,N'-4,4'-diphenylmethylhexane-bis-imide, maleicN,N'-α,α'-4,4'-dimethylenecylohexane-bis-imide, maleicN,N'-m-xylyene-bis-imide, and maleicN,N'-4,4'-diphenylcylohexane-bis-imide. Corresponding monoimides aremade by reacting primary monoamines under similar circumstances with theabove described anhydrides.

In general the N,N' bismaleimides which are described in general FormulaIVa are useful wherein R' and R² are independently selected from thegroups as previously defined.

The diactivated dimethylene compounds having at least 2 hydrogens onseparate carbon atoms which are activated by adjacent carbonyl groupsmay be selected from compounds having the general Formula IIIa and IIIbwhere Z is a carbon-carbon bond; a divalent radical having at least 2carbon atoms up to about 25 carbon atoms which may be alkyl, aliphatic,aromatic, cycloaliphatic, and aromatic or aliphatic groups substitutedwith lower alkyl groups having 1 to 6 carbon atoms; or a divalentradical having at least one carbon atom which is connected to at leastone carbonyl through a heteroatom such as oxygen and nitrogen and thelike as represented in Formula XII wherein R¹⁵ is methylene, alkylene,arylene and R¹⁶ is hydrogen, alkyl and aryl groups having up to 10carbon atoms.

R³ radicals maybe independently selected from any of those monovalentgroups listed in the Table of Formulas listed under XI wherein R⁸, R⁹,R¹⁰, R¹¹, and R¹² are independently selected from hydrogen, halogen,alkyl, arylalkyl, alkoxy, or alkylaromatics.

Polyimide resins have been used to impregnate fiberglass and carbonfiber sheets to form excellent prepregs which are useful in themanufacture of shaped articles and metal clad laminates for use asprinted circuit boards which have resistance to high temperature, lowthermal expansion, and retain a high level of electrical resistivity.

The resins of the invention are particularly useful in manufacturingprepregs which comprise a web of a fiber material coated or impregnatedwith a film or powder of the polyimide resin. Preferably the webconsists of structural reinforcement such as carbon, graphite, boron,steel, silicon carbide, or glass fibers and the like. Fiber reinforcedcompositions of the invention are particularly improved in flowability,i.e. they require a relatively low molding temperature of 177° C., arenon-flammable, have low smoke and toxicity, have improved impactstrength and repairability, are improved in hot wet compression andmoisture resistance, have thermal and mechanical stability. They arealso useful in filament winding.

The polyimides of the invention may comprise mixtures and subsequentreaction products of another ethylenically unsaturated polyimideprepolymer, an epoxy resin, and a curing agent having at least 2 activehydrogens per molecule. Functional blends comprise at least 20% byweight of the polyimide resin of this invention.

The appropriate portions of the polyimide prepolymer made according tothe invention may be mixed directly or physically dispersed with afiller or reinforcing agent, shaped by appropriate means and cured attemperatures ranging from 100° to 250° C. under pressure. A preferredmethod for making fiber reinforced articles is to form a solventsolution of the polyimide prepolymer and mix it with a solution ofanother prepolymer or directly with the reinforcing agent which isthereafter dried to form a polymer coated substrate. When such asubstrate is a woven or non-woven web it is usually referred to as aprepreg. Multilayers of prepregs may be pressed together and cured attemperatures above 100° C. The resin may also be applied to thereinforcing material as a hot melt depending upon the melting point ofthe mixture. In such cases it is preferred to use bisdiketone/bis-imidemixtures that melt below 150° C. to avoid polymerization duringapplication to fibers or fabrics. The addition of vinyl polymerizationinhibitors and/or adjustment of the mol ratio of activemethylene/bis-imide/amine compounds may be used to advantage to controlviscosity. Woven and non-woven webs useful in making prepregs includeorganic or inorganic fibers for example fiberglass, carbon, graphite,boron, carbide coated boron, silicon carbide and organic syntheticfibers.

A prepreg made from the resin of the invention as described above may bepressed together to form a composite of multi-ply laminates which arebonded to a metal foil or resin film on one or both sides to form ametal or film clad laminate.

The resins are also particularly useful in forming shaped articles andclad laminates by reaction injection molding (RIM) techniques and inresin transfer molding (RTM) techniques to produce metal and organicfilm clad laminates using a single injection step. The process involvesplacing a metal foil or plastic film of known thickness on the cavityside of a heated metal mold, placing a fiberglass layer of predeterminedweight over the metal foil or plastic film within the dimensions of thecavity, closing the mold and injecting a reaction injection processableblend of the bismaleimide/bisdiketone prepolymer of the invention intothe mold to impregnate the glass cloth while simultaneously bonding tothe foil to produce a laminate. After a predetermined mold residencetime at a predetermined cure temperature the mold is opened to demoldthe finished clad article.

The metal foils used in making laminates may be selected from copper,aluminum, magnesium, silver, gold, titanium, and steel. Plastic filmsmaybe selected from polyethersulphone, polyether etherketone, nylon,polyester, polyimide, polycarbonate, and polyvinyl fluroide amongothers.

The following preparative examples are intended to serve as non-limitingillustrations of the novel polyimide copolymers, methods for theirpreparation, there use in the manufacture of prepregs and the subsequentuse thereof in the manufacture of metal clad laminates and unlessotherwise indicated all proportions are on a weight basis.

EXAMPLE 1

322 g of maleic N,N'-4,4'diphenylmethane-bis-imide, 181.2 g of1,1'(1,4-phenylene)bis-4-methyl-1,3-pentanedione, 755 g ofdimethylformamide and 26 mls of acetic acid were mixed in a 2-literround bottom flask and heated to 70° C. 0.55 mls of triethylamine areadded and the temperature increased to 80° C. After 2.2 hours theviscosity of the solution increased to 30 cps. and the polymer wasprecipitated in 3-gallons of distilled water, filtered, washed anddried.

A prepreg was made by pulling woven fiberglass cloth (Clark-Schwebel7628 weave with a CS-209 finish) through a dimethylformamide solution ofthis polymer containing 57.9% solids. The prepreg was heated at 150° C.for 10 minutes.

An 8-ply, double-sided copper clad laminate was made from this prepreg.The laminate was made in a press using a temperature cycle of 5 minutesat 150° C., 15 minutes at 170° C. and 40 minutes at 200° C. A pressureof 400 psi was used. The laminate contains 35.6% resin. It was notpostcured and had a room temperature flexural strength of 66,000 psi anda flexural strength of 39,000 psi at 204° C. (after etching the copperoff).

EXAMPLE 2

322 g. of maleic N,N'-4,4'-diphenylmethane-bis-imide, 150 g. of1,1'(1,4-phenylene)bis-4-methyl-1,3-pentanedione, 738 g ofdimethylformamide, 20 g of bis-(4-aminophenyl)methane and 26 mls ofacetic acid were mixed together in a 2-liter round bottom flask andheated to 70° C. 0.55 mls of triethylamine were added and thetemperature increased to 80° C. After 1.8 hours the solution viscosityhad increased to 30 cps and the polymer was precipitated in 3-gallons ofdistilled water, filtered, washed and dried.

A prepreg was made from this polymer as in the previous example from a62.8% solids solution in dimethylformamide. It was heated at 150° C. for10 minutes.

An 8-ply, double-sided copper clad laminate was made from this prepreg.The laminate was made in a press as in the previous example. Itcontained 42% resin. Without postcure it has a room temperature flexuralstrength of 70,000 psi and a flexural strength of 46,000 psi at 204° C.(after etching the copper off).

EXAMPLE 3

322 g of maleic N,N'-4,4'-diphenyl-methane-bis-imide, 176 g of1,1'(1,4-phenylene)-bis-4-methyl-1,3-pentanedione, 459.4 g ofbis-methoxy ethyl ether, 23.2 g of bis-(4-aminophenyl)methane, 26.2 gdistilled water, .12 mls methane sulfonic acid and 0.72 g p-benzoquinonewas mixed together in a 2-liter round bottom flask and heated to 103° C.This solution was cooled to 90° C. and 2.4 mls of triethylamine wereadded. The temperature was increased to 100° C. and after 15 minutes thesolution viscosity was 60 cps. The polymer was precipitated in distilledwater, filtered, washed and dried.

A prepreg was made and postcured as in the previous examples from a66.3% solids solution in dimethylformamide.

An 8-ply, double-sided copper clad laminate was made from this prepregin a press. The laminate was made using a press temperature of 200° C.and a pressure of 400 psig. It was held in the press for one hour. Itwas not postcured. The laminate had a copper peel strength of 8 lbs/inand a water absorption of 25.5 mg on a 2"×2" square.

EXAMPLE 4

112 g of 1,1'(1,4-phenylene)-bis-4-methyl-1,3-pentanedione, 14.8 g ofbis-(4-aminophenyl-methane, and 0.0166 g of p-benzoquinone were mixed ina 500 ml round bottom flask and heated to 120° C. 205.4 g of maleicN,N'-4,4'-diphenylmethane-bis-imide were added over 15 minutes. After 2hours at 120° C. the melt was poured out, cooled and ground.

A 65.0% solids solution of this powder in dimethylformamide was used tomake a prepreg as in the previous examples. The prepreg was heated at150° C. for 10 minutes.

8-ply, double-sided copper clad laminates were made from this prepreg ina press. The press conditions are the same as used in Example 1. Thelaminates were postcured for 1 hour at 200° C. The laminates contained30% resin. Their physical properties are summarized in Table 2.

                  TABLE 2                                                         ______________________________________                                        PHYSICAL PROPERTIES OF -LAMINATES FROM EXAMPLE 4                              PROPERTY              VALUE                                                   ______________________________________                                        Copper Peel Strength (Lb/in)                                                  Room Temperature      7.4                                                     After Thermal Stress  7.4                                                     Volume Resistivity (megohm/c)                                                 After H.sub.2 O Resistance (room temp.)                                                             1.5 × 10.sup.9                                    Surface Resistivity (megohm/c)                                                Dry (room temp.)        1 × 10.sup.9                                    Water Absorption (mg) 22.5                                                    Dielectric Constant   4.6                                                     Dissipation Factor    0.008                                                   Flexural Strength (10.sup.3 psi)                                              Room Temperature      71                                                      ARC Resistance (Seconds)                                                                            181                                                     Machinability (router)                                                                              OK                                                      Solder Float (550° F./10 Secs.)                                                              No Blist.                                               Flammability          V-O                                                     CTE (10.sup.-6 in/in/deg °F.)                                                                6.4                                                     Tg (°C.)       258                                                     ______________________________________                                         ##STR1##

What is claimed is:
 1. The polyimide addition polymer made by reacting(1) a monomer having two methylene groups activated by adjacentcarbonyls with (2) an ethylenically unsaturated bis-imide compound and(3) polyamines selected from a compound having the general formulas NR³R⁵ R⁶ or R⁴ R⁵ N--x--N--R⁶ R⁷, where R³ is independently selected fromhydrogen, monovalent alkyl, aryl, alkyl aryl or alkoxy groups having1-30 carbon atoms and R⁴, R⁵, R⁶ and R⁷ are independently selected fromhydrogen, alkyl, cycloalkyl, aryl, aryl alkyl radicals having up to 20carbon atoms, provided that at least one of R³, R⁴, R⁵, R⁶ and R⁷ mustbe H.